Object of Plasma Physics

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Part I
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• Object of Plasma Physics

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I. Object of Plasma Physics

• 1. Characterization of the Plasma State
• 2. Plasmas in Nature
• 3. Plasmas in the Laboratory

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1. Characterization of the Plasma State
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• 1.1 Definition of the Plasma State
• 1.2 Historical Perspective
• 1.3 Transition to the Plasma State
• 1.4 Examples

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1.1 Definition of the Plasma State
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• 1.1.1 Atomic Physics Brush-Up
• 1.1.2 Thermodynamics Brush-Up
• 1.1.2 Ionized Gases
• 1.1.3 From Ionized Gas to Plasma
• 1.1.4 The Fourth State of the Matter

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1.1.1 Atomic Physics Brush-Up
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How do atoms really look like?
Atoms in a Silicon crystal as seen through a
Scanning Tunnel Microscope
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Looking at an Atom

• An electron cloud

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Looking inside an Atom

• Inside the electron cloud Electrons, Protons
  and Neutrons

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Ionization Process

• Energetic electron causes ionization

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Atomic Structure

• The real proportions inside an atom

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1.1.2 Thermodynamics Brush-up
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• A velocity distribution function represents how
  many particles have a certain velocity
• Example 1 a stream of particles, with
  (one-dimensional) velocities u10.5 (m/s)

f(u)
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u
1
0.5
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Thermodynamics Brush-up (II)

• Example 2 counter-streaming particles, half with
  (one-dimensional) velocities u10.5 (m/s) and
  half with u2-0.5 (m/s)

f(u)
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u
1
0.5
-0.5
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Thermodynamics Brush-up (III)
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• Example 3 a system with a velocity spread and
  density n (m-3).
• In general the distribution is normalized to the
  density
• For a discrete distribution

f(u)
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Thermodynamics Brush-up (IV)
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• Thermal equilibrium all the components of the
  system have the same temperature or average
  kinetic energy
• At thermal equilibrium the velocity distribution
  function becomes a Maxwellian
• The constant A is found by imposing

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1.1.3 Ionized Gases
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• An ionized gas is characterized, in general, by a
  mixture of neutrals, (positive) ions and
  electrons.
• For a gas in thermal equilibrium the Saha
  equation gives the expected amount of ionization
• The Saha equation describes an equilibrium
  situation between ionization and (ion-electron)
  recombination rates.

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Example Saha Equation
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• Solving Saha equation

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Example Saha Equation (II)

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Backup The Boltzmann Equation
The ratio of the number density (in atoms per
m3) of atoms in energy state B to those in
energy state A is given by NB / NA ( gB / gA )
exp -(EB-EA)/kT where the g's are the
statistical weights of each level (the number of
states of that energy). Note for the energy
levels of hydrogen gn 2 n2 which is just the
number of different spin and angular momentum
states that have energy En.
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1.1.4 From Ionized Gas to Plasma
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• An ionized gas is not necessarily a plasma
• An ionized gas can exhibit a collective
  behavior in the interaction among charged
  particles when when long-range forces prevail
  over short-range forces
• An ionized gas could appear quasineutral if the
  charge density fluctuations are contained in a
  limited region of space
• A plasma is an ionized gas that presents a
  collective behavior and is quasineutral

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From Ionized Gas to Plasma (II)

• (Long range) Coulomb force between two charged
  particles q1 and q2 at distance r

q1
q2
r
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From Ionized Gas to Plasma (III)

• (Short range) force between two neutral atoms
  (e.g. from Lenard-Jones interatomic potential
  model)

r
repulsive
attractive
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1.1.5 The Fourth State of the Matter
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• The matter in ordinary conditions presents
  itself in three fundamental states of
  aggregation solid, liquid and gas.
• These different states are characterized by
  different levels of bonding among the molecules.
• In general, by increasing the temperature
  (average molecular kinetic energy) a phase
  transition occurs, from solid, to liquid, to gas.
  
• A further increase of temperature increases the
  collisional rate and then the degree of
  ionization of the gas.

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The Fourth State of the Matter (II)
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• The ionized gas could then become a plasma if the
  proper conditions for density, temperature and
  characteristic length are met (quasineutrality,
  collective behavior).
• The plasma state does not exhibit a different
  state of aggregation but it is characterized by a
  different behavior when subject to
  electromagnetic fields.

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The Fourth State of the Matter (III)
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